Clearly set out the invoicing and payment terms. The service provider should not wait until the end of the assignment or agreement to invoice the customer, but should bill on a monthly basis or upon achieving certain milestones. Billing on a timely basis will help cash flow and establish expectations. Requiring an up-front deposit will also help with cash flow, and will help screen out customers who are unlikely to pay in the end. Also, be clear about what additional expenses (third-party assistance, travel, accommodation, etc.) the customer is expected to bear. The service provider should require payment within, for example, 30 days following the invoice date.